The pathogenesis of peritoneal plasmacytoma development in BALB/c mice appears to involve a genetically-determined component and a pathological tissue microenvironment that selects preplasmacytoma cells. Identification of genes controlling susceptibility is being approached by making BALB/c congenic strains. Mechanisms involved in the selective proliferation of pre-plasmacytoma cells on oil granuloma is being studied in vivo and in vitro. Characterization of the structure of idiotopes on galactan binding myeloma proteins and epitopes on hen egg white lysozyme is being made with monoclonal antibodies and molecular models. New Vk genetic markers are being characterized. Mammary tumorigenesis in wild mouse populations is being characterized.